The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
Hybrid vehicles may utilize an electric machine and an internal combustion engine to selectively produce torque that is transferred to a drivetrain to operate a vehicle. Energy may also be transferred between the internal combustion engine and electric machine. In its normal operation the internal combustion engine of a hybrid vehicle may produce gas emissions. Catalytic converters may reduce exhaust gas emissions in vehicles using an internal combustion engine.
A catalytic converter may be three-way catalytic converter and may include a substrate with a coating of catalyst materials that stimulate the oxidation of hydrocarbons and carbon monoxide, and the reduction of nitrogen oxides, in the exhaust gas. The catalysts may operate optimally when the temperature of the catalysts is above a minimum level. Emissions control using a catalytic converter may be difficult at cold vehicle startup because the catalysts have not reached the minimum operating temperature. Cold start emissions may also be affected by engine-out emissions.
Catalytic converter warm-up time may be reduced at an engine cold start by generating high engine-out energy. The energy may be dependent on exhaust temperature and mass flow rate. Retarding ignition timing and increasing engine idle speed may reduce cold start emissions by increasing these parameters. However, the impact of these strategies may be limited since retarding ignition timing lowers engine efficiency and may eventually result in engine stalling.